Great interest has been generated in the development and use of high definition television (HDTV) systems and the commercial availability of such systems is expected to be widespread throughout the world. In such systems, the aspect ratio (i.e., the ratio of the width of a displayed picture to its height) is greater than that used in conventional, and currently available, non-HDTV television display systems, which latter systems normally provide a display having a 4:3 ratio. It is believed that the use of a video display screen design produces a more cinematic picture presentation to the viewer, such presentation being considered an important advantage in generating interest in potential customers for the wider HDTV display systems.
In order to create a wider screen effect, it has been suggested that an original narrower television image be mapped on to a wider aspect ratio screen in a manner such that the picture that is displayed is "cropped" or deleted at the top and bottom thereof and the central portion will then fit the width of the HDTV display screen. Such a technique, however, eliminates a significant portion of the image and important details thereof would often be deleted.
An inverse problem also arises wherein it is desired to show, on a conventional narrower screen system, an image obtained from a wide screen image source, e.g., a wide screen motion picture film. One approach is to map the wide screen data in its entirety to the small screen format, leaving blank the top and bottom portions of the display screen at each frame, while displaying the entire image across the screen. Such an approach where only a part of the display is used is normally not acceptable to users. Another approach is to use a "pan and scan" technique to select only one region of the total picture area in each frame as being the area of interest and displaying only that portion with a conventional aspect ratio to fill the screen therewith. The original film frames are scanned by an aperture which is narrower than the entire width, the aperture being panned as appropriate to follow the action of interest in each frame. While the entire screen is filled, the complete action or critical image content at the edges of the frame is lost to the viewer.
It is desirable to devise a better technique for handling an image originally made for presentation in one aspect ratio, e.g., a standard 4:3 ratio, so as to convert such image for presentation in a different aspect ratio, e.g., a wide screen HDTV ratio (generally 5:3 or 16:9).